It’s no doubt that electric vehicles are getting more and more popular. But some terms or jargon that manufacturers use in advertisement will make a lot of of people confused.
Today let’s try to clear some of that away and help you choose the right EV for you.
Cell, Module, Pack
Firstly, traditional power batteries can be divided into three main components: cell – module – pack. They progress in layers, where several cell units are packaged into a module, and multiple modules form a battery pack, which we commonly refer to as the “battery pack.”
Cell
The cell is the smallest electrochemical unit within a battery pack, enclosed in a casing. It consists of a positive electrode, a negative electrode, a separator, and an electrolyte—these components form the basis of batteries like lithium-ion or lithium iron phosphate.
The majority of new energy vehicles use lithium-ion and lithium iron phosphate cells, while a few hybrid models employ nickel-metal hydride batteries, predominantly from the Toyota line.
Lithium-ion Batteries(NCM/NCA, or ternary battery) : Typically use lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide as positive electrode materials and graphite as the negative electrode. Variations in the proportion of nickel, cobalt, manganese (or nickel, cobalt, aluminum) in the positive electrode material result in different types of cells, hence the term “lithium-ion.”
- Advantages:
- Higher energy density
- Better lifespan
- High charge/discharge efficiency
- Good performance in low temperatures
- Disadvantages:
- Moderate thermal stability
- Contains heavy and rare metals (cobalt—high raw material cost)
Lithium Iron Phosphate Batteries: As the name suggests, they use lithium iron phosphate as the positive electrode material and carbon or graphite as the negative electrode material in lithium-ion batteries.
- Advantages:
- High safety
- Long lifespan
- Absence of heavy or rare metals (low raw material cost)
- Good performance in high temperatures
- Disadvantages:
- Lower energy density
- Poorer consistency
- Lower performance in low-temperature charge/discharge
Nickel-Metal Hydride Batteries: They use nickel as the positive electrode material and metal hydride as the negative electrode material in a chemical battery (alkaline battery).
- Advantages:
- High safety
- Long lifespan
- Mature technology
- Good performance in low temperatures
- Disadvantages:
- Low energy density
- Low charging efficiency
- High self-discharge
Categorizing by positive electrode materials, as mentioned earlier, there are various types of ternary lithium batteries with different proportions. They are further divided into NCM and NCA routes. NCM refers to positive electrode materials combining nickel, cobalt, and manganese in certain proportions. For instance, in NCM811, the positive electrode material primarily consists of 80% nickel, 10% cobalt, and 10% manganese. Thus, terms like NCM811, NCM622, NCM523 have emerged to represent these battery compositions. Nickel, due to its high capacity, is the most utilized material in ternary lithium-ion batteries. As nickel content increases, the battery’s energy density correspondingly rises. However, this increase leads to a gradual decline in material surface chemical stability and structural stability, resulting in suboptimal cycling performance and thermal stability. Hence, vehicle manufacturers or battery suppliers need to consider their own R&D capabilities when determining the proportion combinations. On the other hand, the positive electrode material in NCA batteries consists of nickel, cobalt, and aluminum, similar in nomenclature and composition to NCM.
Battery Module
Individual battery cells are insufficient to power an electric vehicle. Multiple cells need to be connected in series and parallel to achieve the high voltage and large capacity required to drive an electric vehicle. A module is formed by connecting multiple cells in series and parallel, along with auxiliary structural components that gather current, collect data, and provide secure protection for the cells. This results in a modularized battery assembly.
However, due to this modular approach, it leads to some wasted space in the battery’s structure. Components like wiring and module casings occupy volume, resulting in significantly low spatial utilization.
Nevertheless, with technological advancements, major automotive manufacturers have begun exploring integrated battery technologies (CTP, CTC, CTB). Currently, companies like BYD, Leap Motor, Tesla, among others, have integrated these technologies into their vehicles.
- CTP (Cell to Pack): A module-less battery pack structure technology where the battery pack is integrated into the vehicle’s body floor as part of the vehicle structure. It follows the sequence of cell → battery pack → vehicle body/chassis. Exemplary cases include Contemporary Amperex Technology Co. Limited (CATL), among others. Example: CATL’s third-generation CTP Kirin Battery
- CTC (Cell to Chassis): A technology where cells are directly integrated into the vehicle’s chassis. Part of the battery structure is integrated into the vehicle’s interior floor, enabling high-level integration. Representative cases include Tesla and NIO. Example: NIO’s CTC Technology
- CTB (Cell to Body): CTB is somewhat similar to CTC technology as it involves directly mounting cells onto the chassis. However, the difference lies in CTC treating the battery pack as a separate, protected entity, whereas BYD’s CTB capitalizes on the high safety and structural strength of blade batteries, integrating them into the overall vehicle design. Example: BYD’s CTB Technology
Battery Pack
Pack is essentially the final composition of a battery system, primarily based on several components: battery modules (comprising multiple individual cells forming several modules), casing, electrical systems, thermal management systems, and the Battery Management System (BMS). The entire structural assembly is highly intricate.
- Casing: Comprising the top cover of the battery pack, trays, various metal frames, end plates, and bolts, the casing acts as the “skeleton” of the battery pack, providing support, resistance against mechanical impact and vibration, and environmental protection (water and dust resistance).
- Electrical Systems: Consisting mainly of high-voltage busbars or harnesses, low-voltage harnesses, and relays. The high-voltage harnesses serve as the “main arteries” of the battery pack, continuously delivering power from the heart of the power battery system to various components. The low-voltage harnesses act as the “neural network,” transmitting real-time detection and control signals.
- Thermal Management Systems: There are primarily four types: air-cooled, water-cooled, liquid-cooled, and phase-change material-based. Taking the example of a water-cooled system, it consists of a cooling plate, coolant pipes, insulating pads, and heat-conducting pads. The thermal management system is akin to installing an air conditioning system for the battery pack.
- BMS (Battery Management System): Regarded as the battery’s “brain,” it mainly comprises the Cell Management Unit (CMU) and Battery Management Unit (BMU). Its primary function is intelligent management and maintenance of individual battery units, preventing overcharging and over-discharging, extending the battery’s lifespan, and monitoring its status.
Major automotive companies design and optimize their technologies based on these primary components, introducing their proprietary integrated solutions for the entire battery pack. Examples include GAC Aion’s magazine batteries and Yoyah’s amber battery, all of which are solutions for the holistic battery pack.
Performance Specs of Batteries
Besides the battery type and category, the performance parameters of a battery are also crucial. Terms like battery capacity, charging power, C-rates, and other charging-related terminologies are equally significant for consumers looking to purchase a vehicle. So, what exactly do they mean? Let’s take a look.
- Battery Capacity (kWh): It represents the amount of electrical energy a battery can store, serving as one of the primary indicators of battery size. The unit is kWh, akin to the familiar unit of “electricity usage” or “power consumed.” It directly impacts the parameters of new energy vehicles, notably the driving range, serving as a direct measure of a vehicle’s endurance between charges.
- Energy Density (Wh/kg): This measures the energy a battery can store per unit mass or volume. Batteries with higher energy density can store more energy, providing longer driving ranges within limited space. Thus, enhancing energy density stands as a crucial goal in the development of power battery technology.
- Output Power (kW): It signifies the rate at which charging devices transfer energy to the battery. A higher output power translates to faster charging. Specifically, charging time (in hours) equals battery capacity (kWh) divided by charging power (kW).
- C: This is a measure of charging speed. This metric affects the continuous and peak currents during battery operation and is denoted generally as C (short for C-rate). A higher C-value implies faster charging. The charge/discharge rate is calculated as the charge or discharge current divided by the rated capacity. For instance, with a rated capacity of 150 A·h, discharging at 150A yields a rate of 150/150, which is 1C. Alternatively, describing the time required to fully charge the battery can make it easier to understand. For instance, fully charging in two hours is 0.5C, one hour is 1C, half an hour is 2C, one-third of an hour is 3C, and 5C means charging in one-fifth of an hour, and so forth.
- Voltage: The magnitude of a battery’s operating voltage. Charging power is directly proportional to voltage, increasing which speeds up charging. Recent 800V designs use high voltage to boost charging power. Tesla CyberTruck is rumored to be using1000V architecture.
- Cycle Life: The number of charge-discharge cycles a battery can undergo while maintaining a certain capacity and performance. A longer cycle life means a longer battery lifespan, though this parameter is typically not disclosed by automakers.
- SOC (State of Charge): The battery’s charge state, indicating the remaining power.
- SOH (State of Health): The battery’s health status relative to a new one, considering capacity and available energy.
- Self-Discharge Rate: The rate of capacity loss during storage, often around 1% to 9% per month.
- Internal Resistance: The internal resistance to electric current within a battery, impacting discharge voltage and time. It’s influenced by materials, structure, and manufacturing processes.
- AC Charging: Slow charging method converting AC to DC power, generally at rates of 3.5kW and 7kW, providing more stable battery protection. For example home charging or some public charger.
- DC Charging: Fast charging directly storing DC power into the battery, mostly at 120kW, with some exceeding 480kW.
- Thermal Runaway: Heat generated during charging or discharging that can’t dissipate, potentially causing battery explosion or fire. A good thermal management system is crucial for safety during battery use.